Using HDMI splitters with pen displays


Try to avoid using HDMI splitters if possible. If you need to use one, then understand the limitations and research before you buy one.

Try the alternatives listed at the end of this document.


HDMI splitters are devices that take a single HDMI input and provide two HDMI outputs.

They can be very useful devices, but they are often misunderstood in the context of using pen displays. This doc will help clarify how and if you can use them.

The problem

Often someone with a new pen display will need to connect it to their computer via HDMI.

In this situation they may have an HDMI port but it is already in use.

So, they wonder if an HDMI splitter can turn that 1 HDMI port into 2 HDMI ports. In a sense, that is exactly what an HDMI port does, but it may not do that in a way that is desirable.

What an HDMI splitter does

Physically an HDMI splitter will take a single HDMI port and then provide two HDMI ports.

However, it is important to understand that whatever input the HDMI splitter gets from the computer will ALWAYS be duplicated on the two HDMI ports.

In other words, if you were expecting to show two different things on your pen display and your monitor, then an HDMI port WILL NOT BE HELPFUL. It will always duplicate the exact same image.

If duplication is what you want then an HDMI will work for you.

Your computer thinks of the HDMI splitter as a single display

If you are an HDMI splitter, and you check your computer's settings you will see that it thinks only 1 display is connected. The computer has no idea that the signal is being split.

Native resolutions

Every display device has a native resolution.

It is typically best if the display signal they receive exactly that native resolution

If you pen display and monitor have different native resolutions and yet receive the same display signal, ALWAYS something weird will happen.

You may see an image on one of your displays that is:

  • cropped

  • smaller but with correct proportions

  • smaller but with incorrect proportions - it will looks stretched in one dimension

  • flickering

  • etc.

Or you may not even see an image on one of them at all.

Refresh rate

Your HDMI splitter may not support the refresh rate you want. For example, some might only work at 4K resolution up to 30Hz. Verify refresh rate support before you buy a splitter.

Max resolution

HDMI splitters may not support the resolution of the display signal you want to send. You may want to send a 4K signal, but your HDMI splitter may only support up to 2.5K signal.

All HDMI splitters that I know of support at least 2K resolution (1920x1080)

General weirdness

Sometimes displays just don't like receiving a signal from an HDMI splitter and will show you a blank screen or some other problem.


Your computer may have other ports you can use.

If you have a DisplayPort port available, you can buy a DisplayPort to HDMI adapter. I use these often.

If you have a DVI port, you may be able to find an adapter that works. I don't have any experience with this.

If you have a USB-C port THAT SUPPORTS A DISPLAY SIGNAL, then you could buy a USB-C to- HDMI adapter. I have used one of these and found it to work, but it is flaky - working with some USB-C ports but not others.

Input lag

There are many threads on this, some linked below - and there isn't a clear consensus. Some claim that there is no additional lag, some claim it does. Overall I haven't noticed that splitters that I have personally used have introduce any lag into the signal.

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